Study of the dehydration of Co(H2PO4) 2-2H2O

Abstract

The thermal transformation of Co(H2PO4)2 2H2O was studied under a dry air atmosphere using TG-DTG-DTA. The TG-DTG-DTA curves show that the transformation occurs in three steps, which are dehydration processes. Co(H2PO4)2 · 2H2O and its thermal transformation product were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), and UV-vis near-IR techniques. The nonisothermal kinetics of Co(H2PO4)2 · 2H2O was studied by means of the Kissinger method. The specificity of the thermal transformation was characterized by identification of the bonds to be selectively activated because of energy absorption at the vibrational level, which are confirmed by the comparison of calculated wavenumbers and observed wavenumbers of the FTIR spectra. The activated complex theory has been applied to each step of the reactions, and the thermodynamic functions δH ≠, δG≠, and δS≠ are calculated. These values for three stages showed that they are connected with the introduction of heat and are nonspontaneous processes. © 2009 American Chemical Society.